Materials exhibiting reversible resistance switching are attractive for many of today's semiconductor devices, including non-volatile random-access memory devices. However, previous efforts in the art to reversibly vary electrical performance have exhibited numerous drawbacks. For example, some capacitance-switching semiconductor devices, such as doped Schottky-junction diodes, require relatively large amounts of electrical power (voltage) to switch to, and maintain, a particular capacitance state. Still further, such a device completely loses its capacitance state when the power is withdrawn. Current leakage, and associated heat-build up, are also especially problematic with these switchable semiconductor devices. Thus, high power consumption, current leakage and poor retention characteristics make these devices unsuitable for many practical applications.
Other efforts in the art have taught that several different resistance-switching technologies can be triggered by voltage. This phenomenon has sometimes been called an EPIR (Electrical Pulse Induced Resistance) switching effect. EPIR semiconductor devices are disclosed in U.S. Pat. No. 3,886,577 (Buckley). In the Buckley devices, a sufficiently high voltage (50 V) is applied to a semiconductor thin film in which an approximately 10 micron portion, or filament, of the film may be set to a low resistivity state. Filament size is highly dependant on the amount of current flowing through the device. The device may then be reset to a high resistance state by the action of a second high current pulse (150 mA). However, the set voltage is strongly affected by the number of switching cycles performed. Thus, these devices generally exhibit high power consumption and poor cycle fatigue performance.
Recent efforts in the art have investigated ferroelectric and magnetoresistive materials for non-volatile memory applications. These materials, however, suffer from cycle fatigue and retention problems. Moreover, many magnetoresistive oxide devices require magnetic switching fields and have low operating temperatures.
Some thin film materials in the perovskite family, especially in colossal magnetoresistive (CMR) thin films, have exhibited reversible resistance changes upon application of an electrical stimuli in a magnetic field. It has been recently found that some transition metal oxides in the perovskite family exhibit resistance-switching under a voltage trigger in the absence of a magnetic field. Indeed, the recent observation of the electrical pulse induced resistance (EPIR) change effect in perovskite oxide thin films at room temperature and in the absence of a magnetic field has drawn much attention. See, e.g., “Electric-Pulse Induced Reversible Resistance Change Effect in Magnetoresistive Films,” S. Q. Liu, N. J. Wu, A. Ignatiev, Applied Physics Letters, Vol. 76, No. 23 (2000). In these previous efforts, a Pr1-xCaxMnO3 (PCMO) oxide film placed between two electrodes served as an EPIR device. The resistance states of such simple structured semiconductor devices were switchable by the application of a voltage trigger. The trigger could directly increase or decrease the resistance of the thin film sample depending on voltage polarity. Such voltage triggering phenomenon can be useful in a variety of device applications, including non-volatile memory devices such as resistance random access memory (RRAM) devices.
These early devices, however, required relatively high voltage triggers and the EPIR effect was found to be cycle dependant. The EPIR effect, measured as the ratio between the resistance states, was found to decrease as the number of triggering events increased. Thus, the high power requirements and lack of resistance state stability plagued these early EPIR compositions and devices. Although, the basic mechanism responsible for the EPIR effect is still under investigation, there exist a need in the art to develop improved resistance-switching semiconductor devices for potential application in different technology areas.
Thus, there is a need in the art for resistance-switching semiconductor devices having low power consumption. Still further, there is a need in the art for such semiconductor devices having low voltage leakage and high retention of the respective low and high resistance states. There is also a need in the art for resistance-switching semiconductor devices having improved cycle fatigue performance.